Field
Embodiments of the present invention generally relate to input devices for touch sensing, and more specifically, to input devices that maintain substantially equal capacitive sensing frame reporting rates when operated at different display refresh rates.
Background of the Invention
Input devices including proximity sensor devices (also commonly called touchpads or touch sensor devices) are widely used in a variety of electronic systems. A proximity sensor device typically includes a sensing region, often demarked by a surface, in which the proximity sensor device determines the presence, location and/or motion of one or more input objects. Proximity sensor devices may be used to provide interfaces for the electronic system. For example, proximity sensor devices are often used as input devices for larger computing systems (such as opaque touchpads integrated in, or peripheral to, notebook or desktop computers). Proximity sensor devices are also often used in smaller computing systems (such as touch screens integrated in cellular phones).
When integrated with a display device, such as a tablet or smart phone, the time utilized for sensing is typically interleaved in some manner with display line updates or refresh. Nominal display refresh rate is 60 Hz (or less e.g., 24 or 48 for film, etc.) and may be variable, while sensing frame rate is typically 100-120 Hz and it is desirable for sensing measurement rate to remain relatively fixed as refresh rates and sensing frequencies vary (e.g., to avoid interference). In the event of that display refresh rate is changed, the evenly distributed time periods between display line updates also change, resulting in a corresponding change in the sensing frame rate when it is locked to the display line (e.g., Vblank, etc.) timing. However, accounting for changes in the sensing frame rate is a significant challenge, which increases the device complexity.
This there is a need for an improved input device which more easily handles changes in display rates.